Questions & Answers about Sinun pitää löytää liitu ennen peliä.
Why is liitu in its basic dictionary form here instead of the accusative liidun?
This is because of object case inheritance. When an infinitive verb like löytää is driven by a necessity verb like pitää or täytyy, its total object drops the usual -n ending and takes the nominative-looking form. So you must use liitu instead of liidun.
Why is the word for "you" in the genitive case (sinun) rather than the nominative (sinä)?
Necessity verbs like pitää always require their subject to be in the genitive case. Even though löytää is the action you are actually performing, the grammatical structure of the sentence is dictated by the main governing verb, pitää.
Could I use the partitive form liitua instead of liitu here?
You could, but it changes the meaning. Using the partitive liitua makes it an unspecified amount, meaning "find some chalk". By using the total object form liitu, you are specifically saying you need to find "the chalk" (a specific piece or the whole amount needed).
Why is peli in the partitive case (peliä) after ennen?
The word ennen (before) is a preposition. This is slightly unusual, as most location or time words in Finnish are postpositions. Prepositions in Finnish generally require the word that directly follows them to be in the partitive case.